Silicon controlled rectifier

The invention provides a silicon controlled rectifier comprising a substrate; an N well region and a P well region which are arranged at the first side of the substrate and adjacent to each other; a first N-type doped region and a first P-type doped region which are arranged at the upper surface of the N well region and adjacent to each other; a second N-type doped region and a second P-type doped region which are arranged at the upper surface of the P well region; a first oxidation isolation region which isolates the first P-type doped region and the second N-type doped region; a second oxidation isolation region which isolates the second N-type doped region and the second P-type doped region; an anode end which is coupled with the first N-type doped region and the first P-type doped region; and a cathode end which is coupled with the second N-type doped region and the second P-type doped region. Ion doping concentration of the first P-type doped region is lower than that of the second P-type doped region for eighty percent. According to the framework of the silicon controlled rectifier, sustaining voltage of the silicon controlled rectifier can be effectively enhanced without increasing channel length or using additional auxiliary circuit.